Conventional synchronous drive belts have teeth placed at right angles to the belt mid-circumferential plane such as illustrated in my prior U.S. Pat. Nos. 3,924,481 and 4,108,011. In such belts the whole tooth then engages with a corresponding pulley cavity at the same time, in a manner analogous to a rack and pinion gear. This engagement results in some impact between the belt and the pulley and causes air to be suddenly expelled from the pulley cavity. This in turn results in noise. Spectrum analysis of noise generated by synchronous drive belts typically shows the dominant frequencies being that of tooth engagement, and harmonics of that frequency.
U.S. Pat. Nos. 4,679,459 and 4,951,261 illustrate gear systems having staggered or offset teeth to reduce noise and wear. U.S. Pat. No. 3,033,050 illustrates a belt/pulley combination wherein the belt has teeth in a herringbone design to center the belt over a V-shaped cavity of a pulley in order to preclude axial movement of the belt on the pulley.